gpgme_op_passwd changes the passphrase of the
private key associated with key. The only allowed value for
0. The backend engine will usually popup a window
to ask for the old and the new passphrase. Thus this function is not
useful in a server application (where passphrases are not required
Note that old
gpg engines (before version 2.0.15) do not support
this command and will silently ignore it.
gpgme_op_passwd_start initiates a
gpgme_op_passwd operation. It can be completed by calling
gpgme_wait on the context. See Waiting For Completion.
The function returns
0 if the operation was started successfully,
and an error code if one of the arguments is not valid or the oepration
could not be started.